No Country for Old Men I take it? I wondered the same thing after watching the movie, so I did some research. Turns out there are a couple of companies producing them - how effective they actually are is probably up for interpretation.
the problem is, whether thaty work great, or barley at all, you still have to pay the same tax and paperwork to the atf.
ive heard pf people putting on LONG extentions on their bbls to quiet them down. i think cabellas has them for sale that basicly, replace the choke with another 30" of bbl, and you can daisy chain them too to multiply the effect, and no atf paperwork is required.